C# bmp图像取像素问题

[hzhsky1985]

小弟近日开发一套程序，其中一个功能需要对图像取像素。我用的是.GetPixel方法，但发觉这个方法太慢了（已把扫描的范围尽量缩到最小啦），达不到客户的要求，请问高手有其他更快的方法吗？

[wood87654321]

当然，仔细研究一下Bitmap.LockBits

[hzhsky1985]

我也知道可以用这个方法，也正在研究中，但问题是我还要根据图像和某些条件得到相应点的坐标，如果用Bitmap.LockBits恐怕有点难实现，请教有具体的方法吗

[wood87654321]

很遗憾，没有更快或更直接的办法，你必须自己编程去对应点与数据字节的关系，Bitmap的像素数据结构与BMP文件数据一样并不复杂

[王集鹄]

通过Bitmap.LockBits()方法直接扫描位图的内存

如下代码是取图像透明区域的，供参考：

using System.Runtime.InteropServices;

[DllImport("gdi32.dll")]
public static extern IntPtr ExtCreateRegion(IntPtr lpXform, uint nCount, 
    ref byte lpRgnData);

public static int RGN_AND = 1;
public static int RGN_OR = 2;
public static int RGN_XOR = 3;
public static int RGN_DIFF = 4;
public static int RGN_COPY = 5;
public static int RGN_MIN = RGN_AND;
public static int RGN_MAX = RGN_COPY;

[DllImport("gdi32.dll")]
public static extern int CombineRgn(IntPtr hrgnDest, IntPtr hrgnSrc1, IntPtr hrgnSrc2, 
    int fnCombineMode);

[DllImport("gdi32.dll")]
public static extern bool DeleteObject(IntPtr hObject);

public Region ImageToRegion(Image AImage, Color ATransparent)
{
    //转贴请注明出处ZswangY37(wjhu111#21cn.com) 时间2007-05-25
    if (AImage == null) return null;
    Bitmap vBitmap = new Bitmap(AImage); 
    BitmapData vBitmapData = vBitmap.LockBits(
        new Rectangle(0, 0, vBitmap.Width, vBitmap.Height),
        ImageLockMode.ReadOnly, PixelFormat.Format32bppRgb);
    int vAddress = (int)vBitmapData.Scan0;
    int vOffset = vBitmapData.Stride - vBitmap.Width * 4; // 每行多出的字节数
    int h = vBitmap.Height, w = vBitmap.Width;
    int vTransparent = ColorTranslator.ToWin32(ATransparent); // 透明色
    int vAllocRect = (0x1000 - sizeof(uint) * 8) / sizeof(int); // 预分配的矩形数
    if (h * w < vAllocRect) vAllocRect = h * w;
    Byte[] vBuffer = new byte[sizeof(uint) * 8 + sizeof(int) * 4 * vAllocRect];
    //头信息dwSize\iType\nCount\nRegSize
    uint vCount = 0;
    vBuffer[0] = sizeof(uint) * 8; //dwSize//头信息大小
    vBuffer[4] = 1; //iType//int RDH_RECTANGLES = 1;//数据类型
    IntPtr vResult = IntPtr.Zero;

    uint vPointer = sizeof(uint) * 8;

    bool vWriteRect = false;
    bool vWriteAlways = false;

    for (int y = 0; y < h; y++)
    {
        int vBlockStart = 0;
        bool vLastMaskBit = false;
        
        for (int x = 0; x < w; x++)
        {
            int i = Marshal.ReadInt32((IntPtr)vAddress) & 0x00FFFFFF;
            if (vTransparent == i) // 透明色
            {
                if (vLastMaskBit)
                    vWriteRect = true;
            }
            else
            {
                if (!vLastMaskBit)
                {
                    vBlockStart = x;
                    vLastMaskBit = true;
                }
            }
            if (x == w - 1)
            {
                if (y == h - 1)
                {
                    vWriteRect = true;
                    vWriteAlways = true;
                }
                else if (vLastMaskBit)
                {
                    vWriteRect = true;
                }
                x++;
            }
            if (vWriteRect)
            {
                if (vLastMaskBit)
                {
                    vCount++;
                    WriteRect(vBuffer, ref vPointer, 
                        new Rectangle(vBlockStart, y, x - vBlockStart, 1));
                }
                if (vCount == vAllocRect || vWriteAlways)
                {
                    
                    vBuffer[8] = (byte)vCount;
                    vBuffer[9] = (byte)(vCount >> 8);
                    vBuffer[10] = (byte)(vCount >> 16);
                    vBuffer[11] = (byte)(vCount >> 24);
                    IntPtr hTemp = ExtCreateRegion(IntPtr.Zero, 
                        sizeof(uint) * 8 + sizeof(int) * 4 * vCount, 
                        ref vBuffer[0]);
                    if (vResult == IntPtr.Zero)
                        vResult = hTemp;
                    else
                    {
                        CombineRgn(vResult, vResult, hTemp, RGN_OR);
                        DeleteObject(hTemp);
                    }
                    vCount = 0;
                    vPointer = sizeof(uint) * 4;
                    vWriteAlways = false;
                }
                vWriteRect = false;
                vLastMaskBit = false;
            }
            vAddress += 4;
        }
        vAddress += vOffset;
    }

    vBitmap.UnlockBits(vBitmapData);
    return Region.FromHrgn(vResult);
}

private void WriteRect(byte[] ARGNData, ref uint ptr, Rectangle r)
{
    ARGNData[ptr] = (byte)r.X;
    ARGNData[ptr + 1] = (byte)(r.X >> 8);
    ARGNData[ptr + 2] = (byte)(r.X >> 16);
    ARGNData[ptr + 3] = (byte)(r.X >> 24);
    ARGNData[ptr + 4] = (byte)r.Y;
    ARGNData[ptr + 5] = (byte)(r.Y >> 8);
    ARGNData[ptr + 6] = (byte)(r.Y >> 16);
    ARGNData[ptr + 7] = (byte)(r.Y >> 24);
    ARGNData[ptr + 8] = (byte)r.Right;
    ARGNData[ptr + 9] = (byte)(r.Right >> 8);
    ARGNData[ptr + 10] = (byte)(r.Right >> 16);
    ARGNData[ptr + 11] = (byte)(r.Right >> 24);
    ARGNData[ptr + 12] = (byte)r.Bottom;
    ARGNData[ptr + 13] = (byte)(r.Bottom >> 8);
    ARGNData[ptr + 14] = (byte)(r.Bottom >> 16);
    ARGNData[ptr + 15] = (byte)(r.Bottom >> 24);
    ptr += 16;
}

private void button1_Click(object sender, EventArgs e)
{
    Region = ImageToRegion(pictureBox1.Image, Color.FromArgb(216, 233, 236));
}

[hzhsky1985]

谢谢楼上各位，具体的方法我已想到，但可不可行就要靠我慢慢调试了，这里再问一下，用Bitmap.LockBits()取边缘，可行吗？

[hzhsky1985]

还有一个地方不理解的。
p[0] = p[1] = p[2] = 255;
p += n;
p+=n这句是什么意思。

[hzhsky1985]

自己顶一下，上面的写错了，我意思是
nt n = 3；
int w = pictureBox1.Image.Width;
int h = pictureBox1.Image.Height ;
Color c;
Graphics f = pictureBox1.CreateGraphics();
// bmp = new Bitmap(w, h, PixelFormat.Format1bppIndexed);
// pictureBox1.Image = bmp;
bmp = new Bitmap(pictureBox1.Image);
BitmapData data = bmp.LockBits(new Rectangle(0, 0, w, h),ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
unsafe
{
// 将原始图片变成灰度二位数组
byte* p = (byte*)data.Scan0;
byte[,] vSource = new byte[w, h];
int offset = data.Stride - w * n;

for (int y = 0; y < h; y++)
{
for (int x = 0; x < w; x++)
{
vSource[x, y] = (byte)(((int)p[0] + (int)p[1] + (int)p[2]) / 3);
p += n;
}
p += offset;
}

bmp.UnlockBits(data);
// 将灰度二位数组变成二值图像
bmpDest = new Bitmap(w, h, PixelFormat.Format24bppRgb);
BitmapData dataDest = bmpDest.LockBits(new Rectangle(0, 0, w, h), ImageLockMode.WriteOnly,
PixelFormat.Format24bppRgb);

p = (byte*)dataDest.Scan0;
offset = dataDest.Stride - w * n;
for (int y = 0; y < h; y++)
{
for (int x = 0; x < w; x++)
{
p[0] = p[1] = p[2] = (int)GetAverageColor(vSource, x, y, w, h) > 120 ? (byte)255 : (byte)0;
p += n;
}
p += offset;
}

bmpDest.UnlockBits(dataDest);
pictureBox1.Image = bmpDest;

}
这是一个变为二值化的代码，我想问其中的p += n这句是什么意思

[王集鹄]

n = 3 ....

对于24位色的位图，一个像素需要24个bit表示--即：3个byte(24 / 8)
这里的n就表示访问下一个像素需要偏移几个字节。。。
BitmapData.Scan0属性表示第一个像素(注意第一个像素是在左下角)存放的内存地址。。。

[huang_8228]

p += n就是p = p+n